The invention relates to the purification of polyether polyols and polyalkylene carbonate polyols. More specifically, the invention relates to the removal of alkaline catalysts from polyether polyols and polyalkylene carbonate polyols.
Polyether polyols are conventionally produced by the addition-polymerization reaction of an alkylene oxide with an organic compound having at least one active hydrogen atom in the presence of an alkaline catalyst. Polyalkylene carbonate polyols are conventionally produced by the addition-polymerization reaction of an alkylene carbonate, or alkylene oxide and CO.sub.2, with an organic compound having at least one active hydrogen atom in the presence of an alkaline catalyst. The resulting reaction mixtures, therefore necessarily contain substantial amounts of these alkaline catalysts. The presence of the alkaline catalysts remaining in the polyether polyols or the polyalkylene carbonate polyols adversely affect the performance thereof in their intended uses such as raw materials for the production of polyurethanes, hydraulic liquids, cosmetics, surfactants, synthetic lubricants and the like.
There are several known methods for the removal of these alkaline catalysts from the polyether polyols or the polyalkylene carbonate polyols. Present commercial practices for the removal of these impurities can involve neutralization of the alkaline catalysts with acids forming insoluble salts and removal of these salts by filtration. Centrifugation, employing mixtures of polyol, water and solvent, can also be employed for the removal of residual catalysts.
The crude polyols without prior neutralization of the catalyst can be treated with a synthetic type adsorbent followed by filtration of the polyol. Present commercial practice involves mixing the polyol and adsorbent with an amount of water ranging from 0.05 to 5.0 percent. Often the polyol quality suffers because of the great risk of oxidizing the polyols due to repeated interruption in the filtration process necessitating a break in the filter press. This attendant exposure to air causes the production of off-grade polyol by increasing undesirable acidity.
A number of patents disclose the use of various acidic materials for the neutralization of the alkaline catalyst followed by filtration of the precipitated salts. Among these are U.S. Pat. Nos. 3,833,669; 3,053,903; 2,983,763; 2,448,664; and 3,016,404. U.S. Pat. No. 3,528,920 discloses the use of synthetic magnesium silicate as an adsorbent for the removal of the catalysts from the various glycol ethers. However, this patent also discloses that the undesirable alkaline catalyst is first neutralized with acid prior to filtration.
The present processes known for removal of alkaline catalysts from polyether polyols and polyalkylene carbonate polyols have several attendant disadvantages. In many of the processes, water is present during the catalyst removal. This results in undesirable and unwanted hydrolysis of the polyols. Further, several of these processes require relatively high temperatures in order to purify the products.
What is needed is a process for the removal of alkaline catalysts from polyether polyols and polyalkylene carbonate polyols in which water is not present and which is carried out at reasonably low temperatures.